In a charge-coupled device (CCD) type or an amplification type solid-state imaging device used in a digital still camera, a cam coder or the like, there is a demand for finer pixels to obtain a high definition image. However, the finer the pixels, the smaller the light receiving area of a photoelectric conversion element for detecting light included in the pixels, resulting in a reduction in sensitivity.
Japanese Patent Application Laid-Open No. 2006-191081 discusses complementary metal-oxide-semiconductor (CMOS) type, which is also an amplification type, solid-state imaging device of a construction in which a first substrate with a photoelectric conversion element and a transfer transistor arranged thereon and a second substrate with another circuit arranged thereon are bonded to each other to form a solid-state imaging device to secure the requisite light receiving area of the photoelectric conversion element.
Further, Japanese Patent Application Laid-Open No. 2006-191081 discusses a solid-state imaging device in which a connection portion extending through a second substrate is connected to an input/output pad to effect connection of the input/output pad from the back-side of the second substrate. This input/output pad is formed after the connection portion is exposed by polishing of the second substrate.
However, Japanese Patent Application Laid-Open No. 2006-191081 discusses a construction in which the input/output pad is directly connected to the circuit of the first substrate. In such a construction, external noise from an external terminal is imparted to the circuit of the first substrate, so that a malfunction of the circuit can be generated. Further, a photoelectric conversion element is arranged on the first substrate, and incorporation of external noise may affect the image signal.